The most common and most likely answer to this crossword clue is the 8 letter word PRIMEVAL
I've seen this crossword clue in Financial Times
P
R
I
M
E
V
A
L
More clues leading to the result PRIMEVAL
- Being proper, wash up early
- Old and prudish, oddly enviable
- Very early in toilet, turning up after five, say
- Formal English girl, in short, of ancient origins?
- Ancient Byzantine vampire near lake
- Old, quiet doctor overwhelmed by adversary
- First in time, grotesque vampire draws a number
- Vampire bats left earliest
- Proper English girl before Man came along?
- Ancient vampire rowing on lake
Buddy explains!

The straight part
We know that "before Man came along" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case before man came along = primeval.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PRIMEVAL mean?
PRIMEVAL adjective- Belonging to the first ages
- Primary; original
- Primitive